An Anson man convicted of murdering another man during a 2009 drug deal is asking a federal court to release him from prison on grounds that the evidence presented at his trial was insufficient — his fourth attempt to get his 2012 conviction overturned.

Robert Nelson, 45, asked the U.S. District Court in Bangor to “vacate the illegal conviction of an innocent man,” according to a petition for writ of habeas corpus filed Monday.

Nelson, who was convicted in 2012 and sentenced to 45 years in prison for the shooting death of Everett L. Cameron, previously filed a motion for a new trial in Somerset County, appealed his conviction before the Maine Supreme Judicial Court and also filed a post-conviction appeal. All were denied.

In the new filing, Nelson, who is representing himself, argues that a lack of DNA evidence, the state’s failure to produce a murder weapon and a lack of evidence about what happened at the murder scene between the time Nelson admitted meeting with Cameron and the time he was found dead, are all grounds for his claim that the state did not meet the required burden of proof.

He also writes that prosecutors linked one witness account of a gunshot in the area to the murder although there was no evidence to prove that the gunshot the man heard was the one that killed Cameron.

During the 2012 trial, the state argued that Nelson was a drug addict who was under the influence of pills and alcohol when he met with Cameron on Town Farm Road in Anson to get oxycodone and shot him in his truck. Nelson later showed up at his 4-year-old daughter’s birthday party incoherent and high on drugs.

But Nelson’s DNA was never found in Cameron’s truck and two DNA samples belonging to unidentified males were never investigated, according to the petition filed by Nelson. A murder weapon was never produced.

Witnesses at the trial testified that they saw Nelson at his daughter’s birthday party around 2:15 p.m. the day of the murder — about two hours before Cameron’s body was discovered — and the state failed to explore whether Cameron was still alive after meeting with Nelson and what may have happened between 2:15 and the time when his body was discovered around 4 p.m., according to the filing.

Testifying on his own behalf, Nelson told the court that on the day of Cameron’s death, he met with him to tell him he didn’t have the money he owed him but did not kill him. Cameron was found dead around 4 p.m. that afternoon after his girlfriend, Virginia Hayden, grew worried that he had not returned home and discovered his truck down the road.

Nelson’s trial attorney, Phil Mohlar, told the court in 2012 that state police never looked at anyone but him as a suspect and conducted a poor investigation.

“Cameron was reaching out to people that day and had contact with other people in the drug community. He made calls to other people. What about those people who called Cameron before Rob? What if they made arrangements with him?” Mohlar said.

John Nivison, then a Somerset County Superior Court justice, decided the case in a jury-waived trial and said that even without a murder weapon, DNA evidence and eyewitness accounts, the state’s circumstantial evidence against Nelson was sufficient to prove him guilty.

In his 2013 appeal to the Maine Supreme Judicial Court, Nelson also argued that there was insufficient evidence in the trial to convict him, but a panel of six judges contradicted the argument, saying there was ample evidence to find him guilty beyond a reasonable doubt.

“This is not a case where the testimony or evidence is in dispute, what’s in dispute is the way the trial judge, sitting as the fact finder, unreasonably interpreted those facts and completely abandoned the presumption of innocence,” Nelson wrote to the federal court.