"Michael was not feeling well the night before… the doctor was summoned," Oxman told Robin Roberts on "Good Morning America" today. "I don't know why."
"I don't want to jump to conclusions, and I don't want to point fingers," Oxman said. "We don't know what Michael Jackson perished from, but what I do fear is that it was the medications."
Oxman, who was at the hospital with the Jackson family when he died, said Jackson first started taking pain medication after his hair caught fire during the filming of a Pepsi commercial in the early 1980s. The drugs subsequently became a regular part of his life when Jackson later fell off a stage and suffered a broken leg and a cracked vertebrae.
"I spoke to family members. I said if this situation arises where Michael perishes because of these medications ... I will not hold my tongue," Oxman said. "I will speak out and I will speak out loud about the overmedication of Michael Jackson."
Oxman noted that the stress of Jackson's upcoming tour may have put him under tremendous pressure.
"Michael was rehearsing and working extremely hard," he said. "I think he was in discomfort because he was working so very hard."
Jackson's 2005 trial on child molestation charges also created a burden on the star that Oxman said changed him for good.
"I don't think that Michael ever fully recovered," he said.
Defense attorney Ben Brafman, who represented Jackson during that case, agreed.
"When I knew him during the trial, he was extraordinarily frail physically and emotionally unstable -- a 45-year-old 12-year-old," he told ABC News. "So thin and gaunt -- it was almost impossible for me to imagine him going through a grueling trial proceeding."
Brafman added Jackson "didn't strike me as someone who could survive much longer."
Family friend Mark Lester, also the godfather of Jackson's three children, said he never saw any signs of Jackson's use of prescription pain medication or that he was in ill health in the days leading up to his death.
"There was no indication of anything other than Michael focusing his everything on this set of concerts," he said from London this morning.
Lester said that, if called to do so, he would absolutely step up to care for Jackson's children, Prince Michael I, Paris and Prince Michael II, but that there would be no shortage of people willing and able to take them in.
"Michael has a large family," he said. "I'm sure the children will be well looked after."
Lester said he was unsure if the children had been told about their father's death.
"The kids were everything to Michael. They were his whole life," he said. "He was a very active and involved father."
The Los Angeles Fire Department was called to Jackson's residence at 12:26 p.m. PT Thursday. Paramedics performed CPR on Jackson, who was not breathing when they arrived at his home. He was rushed to L.A. Medical Center, six miles from his home.
Oxman said there was complete pandemonium at the hospital where Jackson was pronounced dead after doctors worked on him for more than an hour.
"Nobody knew what was happening," he said. "We couldn't even speak."
While Jackson's family and friends were inside the hospital trying to understand a life without Jackson, fans began to gather outside.