(Reuters) - The drug PCP can cause a trance-like state and violent behavior, a doctor said on Monday at the murder trial of ex-NFL star Aaron Hernandez, in testimony about the drug that may have been used by two friends of Hernandez the night of the killing the threesome are accused of committing.

Dr. David Greenblatt, a professor at Tufts University School of Medicine, said the drug also known as angel dust can make people sweaty or shaky, and hinder cognition and the ability to distinguish what is real from what is not.

"It can cause violent behavior," he said. Greenblatt was the first witness to testify for the defense in Hernandez's trial, which began in January. 

Hernandez, 25, has pleaded not guilty to murder and firearms charges in the killing of Odin Lloyd, a semiprofessional football player who was dating the sister of his fiancée. If convicted, he faces a maximum penalty of life in prison.

Prosecutors say Hernandez, who played tight end for the New England Patriots, and two friends, Ernest Wallace and Carlos Ortiz, picked up Lloyd at his Boston home in the early hours of June 17, 2013, and drove him to an industrial park near Hernandez's house in North Attleboro, Massachusetts.

The victim's bullet-riddled body was found in the industrial park later that day.

Prosecutors rested their case against Hernandez last week after calling more than 120 witnesses. Wallace and Ortiz have also been charged with murder and will be tried separately. They have pleaded not guilty.

Earlier in the trial, Jennifer Mercado, a cousin of Hernandez, testified that Wallace and Ortiz appeared jittery and sweaty when she saw them before the murder. She said they behaved similarly to when they had used PCP previously.

A report by Rolling Stone magazine in 2013 after Hernandez was arrested claimed he was a heavy user of angel dust, and had become so paranoid that he carried a gun wherever he went.

On Monday, Greenblatt said the manifestations of the drug can last from a few hours to weeks or months. "They can appear and disappear quickly and unpredictably over a period of time," he told defense attorney Charles Rankin.

Defense attorney James Sultan said earlier that the defense team planned to call three witnesses before resting their case, and that they expected the testimony to conclude midday on Monday.

Hernandez had a $41 million contract with the Patriots. He was dropped from the team hours after his arrest in June 2013.