When the former Giants safety Tyler Sash was found dead at age 27 of an accidental overdose of pain medications at his Iowa home on Sept. 8, his grieving family remained consumed by a host of unanswered questions about the final, perplexing years of Sash’s life.

Cut by the Giants in 2013 after what was at least his fifth concussion, Sash had returned to Iowa and increasingly displayed surprising and irregular behavior, family members said this week. He was arrested in his hometown, Oskaloosa, for public intoxication after leading the police on a four-block chase with a motorized scooter, a pursuit that ended with Sash fleeing toward a wooded area.

Sash had bouts of confusion, memory loss and minor fits of temper. Although an Iowa sports celebrity, both as a Super Bowl-winning member of the Giants and a popular star athlete at the University of Iowa, Sash was unable to seek meaningful employment because he had difficulty focusing long enough to finish a job.

Barnetta Sash, Tyler’s mother, blamed much of her son’s changeable behavior, which she had not observed in the past, on the powerful prescription drugs he was taking for a football-related shoulder injury that needed surgery. Nonetheless, after his death she donated his brain to be tested for chronic traumatic encephalopathy, or C.T.E., a degenerative brain disease caused by repeated trauma that has been found in dozens of former N.F.L. players.