AUGUSTA — A defense attorney warned jurors Tuesday that they will see “terrible pictures, terrible videos” in connection with the case of a Sidney man who faces 21 separate charges including rape and sexual exploitation of a 4-year-old girl.

But that attorney, Ronald Bourget, also asked jurors to keep an open mind, saying that his client, Eric L. Bard, has an abnormal condition of the mind and lower intelligence than they have.

“Mr. Bard only has so much aptitude, he only has so much cognitive ability,” Bourget said in his opening statement. “He suffers from pervasive developmental disorder.”

He said at least one psychologist would testify during the trial about Bard’s mental limitations.

In Bourget’s opening statement, he described his client as “a 24-year-old man from Sidney sitting at the defense table bobbing and weaving with long hair who has the attention span of maybe an hour,” and who was the subject of investigations by a number of agencies from the Maine State Police.

The prosecutor, Assistant Attorney General Paul Rucha, had already told the jurors in his opening that they would see disturbing images of an adult engaging in the sexual assault of a young girl. Rucha reminded the jury that under state law, children under 12 years old cannot consent to have sex with an adult.

Rucha said the child would not testify during the trial, but her mother planned to take the stand.

Bard, 24, had pleaded not guilty and not criminally responsible to all 21 charges in the indictment against him, most of which carry maximum 30-year prison terms.

He is accused of sexually assaulting the child he was babysitting and recording the acts in 2011 and 2012.

Before the jurors entered the courtroom, Bard withdrew the not criminally responsible plea. The judge told Bard that he understood the plea withdrawal “was based on lack of evidence in that regard.”

Bard answered “Yeah” several times in response to the judge’s questions. Jurors on Tuesday were assembled in an adjacent room as the final pretrial motions were handled in front of Justice Donald Marden in Kennebec County Superior Court.

Before the trial started, Bourget attempted to get the judge to reverse his order in which he refused to suppress evidence seized by police.

Two detectives with the Maine State Police Computer Crimes Unit, David Armstrong and Justin Kittredge, testified about receiving consent to search the Bard home two years ago for computers and other items that might contain child pornography.

For the start of the trial, Bard, who has long, wavy brown hair, wore long red pants, and a blue, red and tan short-sleeved shirt. He kept a gray sweatshirt wrapped around his hands. He was not shackled or in handcuffs.

He watched his mother, Jeanne Bard, testify about the June 19 search of her home, saying police wanted all the computers in the house. She carried out her daughter’s computer for them.

“Actually, I didn’t know what was going on,” she said on the witness stand.

Bourget sought again to keep images found on a storage disk from coming into evidence.

The investigation into Bard began with a tip about an ad on Craigslist offering baby-sitting and bathing services for young kids in June 2012 and ended with serious sexual abuse charges against Bard.

Amy Forbus testified she was on Craigslist in May 2012 seeking daycare for her son because she and her husband were both working full-time.

“I came across an ad I just thought was creepy,” she said. She contacted Maine State Police, she said, and later forwarded the ad to them because it was flagged and then removed from Craigslist.

Police traced the ad to Bard’s residence in Sidney, where he initially denied and later admitted placing the ad, according to Maine State Police Detective Michael Joseph Chavez, who was one of several investigators who spoke to Eric Bard on June 19, 2012, the day computers and other devices were seized.

Chavez testified he spoke to Bard in what appeared to be a mud room that was used by Bard as a bedroom.

He said Bard was rocking in a recliner chair, his fingers interlaced as he responded to questions, but was getting more disturbed when they asked him about child pornography. “At one point he lifted up his glasses and wiped a tear from his eye,” Chavez said.

Chavez identified Bard in the courtroom and told one of the prosecutors, Assistant District Attorney Kristin Murray-James, that said his appearance Tuesday was different from his first encounter more than two years ago.

“His hair is longer,” Chavez said. “It appears he has facial hair and he may have put on a couple of pounds.”

Bard is accused of sexually assaulting the girl in Augusta between December 2011 and April 2012.

As the clerk read all the charges in the indictment to the jury, she included numbered references to specific photographs and videos related to the charges of sexual exploitation of a minor.

The charges say Bard did “employ, solicit or entice, persuade, use or compel” the child to engage in sexually explicit conduct with the intention of photographing it.

Bard has been held in jail or at Riverview Psychiatric Center, where he has undergone a series of competency evaluations, since his arrest in late July 2012.

In the two years since Bard was charged, he has been to court a number of times as Bourget and his other attorneys, Gina Yamartino and Darrick Banda, sought to have him found incompetent to enter a plea and then incompetent to stand trial.

Bard was evaluated by psychologists with the State Forensic Service and private forensic psychologists, and found competent to proceed to trial. The prosecutor, Assistant Attorney General Paul Rucha, maintained that Bard was competent to stand trial on 11 charges of sexual exploitation of a minor, seven charges of gross sexual assault, two charges of unlawful sexual contact and one charge of assault.

Bard, who is 4-foot-10 with long hair and a beard, typically keeps his head down and his face hidden by his hair in the courtroom. Most of the time he rocks slowly forward and back, appearing to take little interest in courtroom proceedings.

In a ruling issued Aug. 14, Marden rejected a defense bid to suppress evidence gleaned from a small computer storage device. In his written order, Marden described the circumstances of the seizure, saying law enforcement agents became interested in it after Bard objected to them examining the device because there was “personal information on it.”

Investigators seized the device on June 19, 2012, and obtained a search warrant to view its contents 10 days later.

Bard’s attorneys said he was not competent to answer questions when he told officers that his computers contained child pornography.

Marden’s ruling said he viewed a recording of the June 19 questioning that took place in Bard’s bedroom and on the lawn of the house he shared with his mother.

“While his answers were slow in coming, he responded in a conversational tone with details that were appropriate to the questions … It took some time for the defendant to realize that the interest of the officers was in finding something ‘inappropriate’ on his computers. At this point he started asking questions about the seriousness of the conduct and length of jail sentences. Nevertheless, he continued to answer questions and was completely cooperative until the SD card came into play.”

Marden ruled that “the court is satisfied the defendant’s constitutional rights have not been violated or any violations were harmless under the doctrine of inevitability.”

A woman selected as one of 15 jurors was dismissed early Tuesday — it was not clear why — prior to the start of the trial and took a seat briefly in the rear of the courtroom.

Two alternates remain on the jury of 10 women and four men.

The judge told jurors previously that the trial is likely to take four days.