AUGUSTA — William Lord spoke to a Maine State Police trooper on the phone, saying he had not cared for his infant son the previous night. He also wanted to know why bright lights were shining into his windows and why he needed to come outside and talk with police.

Lord, 40, asked repeatedly if he would be arrested. He talked about a lawyer coming to his home as well as needing to put his daughter on a school bus.

About 19 minutes of that conversation between Lord and Trooper Mark Ferreira on Oct. 20, 2014, was played in a courtroom Tuesday at the Capital Judicial Center, where a jury is hearing evidence in his trial. Lord is accused of committing aggravated assault and domestic violence assault on a child less than 6 years old – his 3-month-old son, Preston – on Oct. 19, 2014, in Wayne, according to an indictment.

Lord has pleaded not guilty, and his trial in front of eight women and five men continues Wednesday. Justice Robert Mullen told the jurors they could expect to hear closing arguments in the case Thursday.

The baby’s mother, Ericka Melanson, was the first witness Tuesday, testifying that the baby, who was born July 21, 2014, was in a child safety seat – but not buckled in – when Lord threw him down the flight of wooden stairs, cursing at her after they argued about her texting another person. She said the baby was ejected from the seat and landed face first, and initially wasn’t breathing.

She drove the baby to MaineGeneral Medical Center in Augusta, where he was diagnosed with a skull fracture.

Before the incident, Lord had been fired from his job as a registered nurse at Riverview Psychiatric Center. The firing followed a review of a December 2013 incident in which Lord approved the use of pepper spray by a state corrections officer on forensic patient Arlene M. Edson. The woman was left for hours in restraints with the irritant on her skin, despite being compliant and not threatening the staff, according to a report.

Lord is no longer working as a nurse. He agreed to have his nursing license placed on inactive status in an August 2015 consent agreement with the state Board of Nursing.

On the audiotape of the call played Tuesday at his trial, Lord tells trooper Ferreira that he assumes the police are there because of Ericka. “The only thing I know is that that woman is a compulsive liar,” Lord told the officer.

He talks about making coffee, about having to use the bathroom, and asks about Preston.

“The baby’s got a few minor bumps and scratches,” Ferreira said, adding that the child would be OK.

Melanson testified that she and Lord had met at Riverview Psychiatric Center, where Lord was a nurse and she was hired initially as a custodian but then moved into a mental health worker position.

She said she and Lord had a sexual relationship and then an emotional one, despite his living with his fiancee and their two children. Melanson said she wanted to have a family with Lord after learning she was pregnant.

She moved into in Lord’s Wayne home with him and his fiancee and their two children and another daughter of Lord’s for about three weeks after Preston was born, but then returned to her Augusta apartment.

Melanson said she, her 2-year-old daughter and Preston had gone to Lord’s house the night of Oct. 19, 2014, after Lord texted her, telling her to bring him dinner and cigarettes.

She said she had been using his car because hers was being repaired.

She said Lord had been drinking alcohol, couldn’t stand up and tried to light a cigarette backward and that they argued at the kitchen table while she was sending someone a text message. She told him – and later another detective – that she was texting with a girlfriend, but was really exchanging texts with a man who was a friend.

She said Lord later reached for her phone to see whom she sent the texts to, but she objected. Melanson said Lord became angry and was yelling and swearing. “He told me he didn’t want me in this bedroom,” she said.

Melanson said Lord then threw the baby and the car seat down the stairs and threatened to throw her down as well. She said she felt Lord’s foot on her back as she ran down to the baby.

“I picked him up and I sat on the couch with him, and he started to cry,” she said of Preston.

Melanson said she called a girlfriend to try to get a ride to the hospital but ended up taking Lord’s vehicle instead.

On Tuesday afternoon, Dr. Rosamund Davis, a pediatric hospitalist at MaineGeneral, testified that Preston had a swollen area on his scalp, and that a CT scan shows a linear skull fracture. She put her hand up to the right side of her head and touched an area toward the back of her head and up high.

She said laboratory test results and a physical examination showed no other signs of trauma.

Lord is represented by attorneys Robert Ruffner and David Zirschky. In his opening statement Tuesday, Ruffner told jurors that the state will be unable to prove beyond a reasonable doubt that Lord threw the baby down the stairs.

He said Melanson “did not want my client to go back to his fiancee and continue that relationship.”

The prosecutor, Assistant District Attorney Kristin Murray-James, began her opening statement by showing jurors an enlarged color photo of Preston. Later, she showed them photos of the interior of Lord’s Wayne home, including ones showing a flight of 10 wooden stairs that she said was where the car seat was thrown while Preston was in it.

She told jurors that Lord told Melanson to “get out of the house and take Preston with you.”