The son-in-law of Philip McCloskey described for a federal jury Thursday how he came upon the 69-year-old’s body in a secluded area in Marshfield in 2001, just days after McCloskey had been stabbed to death and left in a pile of leaves by serial killer Gary Lee Sampson.

“I did notice, out of the corner of my eye, what I thought to be a hand sticking in the air,’’ said Patrick Shea, who married McCloskey’s daughter Cheryl 15 years ago.

He recounted how he alerted the police officers who had organized the search for McCloskey’s body in woods off School Street, then ran to Cheryl.

“I ran through the briars and the brush to get to her and her sister . . . to console her and prevent her from seeing what I had seen,’’ Shea told jurors.

Shea testified in Sampson’s death penalty trial in US District Court in Boston. He was the first witness called who had a personal connection to Sampson’s crimes.

Sampson, 57, faces the death penalty for killing McCloskey, a father of six from Taunton, and 19-year-old Jonathan Rizzo during a rampage over several days in July 2001.

He also killed Robert “Eli’’ Whitney, 58, in New Hampshire that same week. He was convicted in that state for that crime, but jurors in the federal case in Boston can also consider that crime when deciding whether to mete out a death sentence.

Sampson has admitted to the killings and been convicted. A jury sentenced him to death in 2003, but a federal judge vacated that decision after he found juror wrongdoing. Now, prosecutors are again seeking a death sentence, while defense attorneys are arguing for life without parole.

On Thursday, the second day of the sentencing trial, several investigators described the remote area where McCloskey’s body was found and testified about how hard it would have been for him — he months earlier underwent quintuple bypass surgery — to be forced by Sampson to climb the hill.

Under cross-examination by Sampson’s defense attorneys, the investigators also acknowledged that Sampson had provided information about the location of evidence, such as McCloskey’s wallet and keys.

Sampson’s lawyers have argued that Sampson ultimately confessed and cooperated with authorities because he felt guilt for what he had done, a personality factor that argues against imposing the death sentence.

In a 90-minute taped confession that was played for jurors, Sampson recounted his crimes, including how he hitchhiked a ride from McCloskey in Weymouth, and put a knife to him and told him to drive toward Marshfield.

“I told him, if he even thinks about it, I would hurt him,’’ Sampson said, according to the recording.

Milton J. Valencia can be reached at milton.valencia@globe.com. Follow him on Twitter @miltonvalencia.