Nearly seven years after a federal jury recommended that Gary Lee Sampson be sentenced to death for carjacking and killing two motorists during a weeklong 2001 series of killings in two states, lawyers for the Abington man plan to argue in court today that he should get a new trial.

The legal team for Sampson, who would be the first person executed for a crime in Massachusetts since 1947, contend in a 155-page motion that his constitutional rights were violated because his trial lawyers were ineffective.

His new lawyers say defense attorneys failed to give the jury a full picture of Sampson’s history of mental illness and traumatic brain injuries dating to childhood and that the evidence would probably have discouraged jurors from recommending the death penalty in December 2003.

Sampson had pleaded guilty to the murders, leaving the jury only to decide whether he should be executed.

“Trial counsel … never adequately investigated available witnesses and documents that establish brain damage and mental disease far greater than that presented at trial and childhood trauma and brutal conditions of confinement starting in his teenage years that coalesced to exacerbate this brain damage and its accompanying psychiatric impairments,’’ said the brief filed by Sampson’s legal team.

The team that will appear before US Chief District Court Judge Mark L. Wolf includes attorneys from Williams & Connolly LLP, the Washington firm that successfully defended President Clinton at his impeachment trial and represented Vice President Dick Cheney in the Valerie Plame investigation.