JACKSONVILLE, Fla. -- Adrian Smith testified Thursday at his murder trial that he thought of the 4-month-old victim as his son, even though he was not his biological father.

Prosecutors said Smith lost his temper and stuffed a baby wipe down the boy's throat to suffocate him.

Smith, 36, is charged with second-degree murder. He has been held without bond since days after the baby's February 2006 death.

Smith testified that he loved the child as his own -- even named the boy Adrian Smith Jr. -- and that the death was an accident.

"Being that the father of the child wasn't going to be there, I took on that responsibility of being his dad," Smith said. "It's a great honor."

On the stand, Smith said that on the day the boy died, he had given him a bottle and put a wipe on his chest. He then noticed the child gagging and having trouble breathing and took him to Wolfson Children's Hospital.

Doctors found a baby wipe lodged in the boy's throat.

White said he broke down and cried when doctors told him the baby had died.

"I love my son," Smith testified. "I would not do that to my son."

Earlier in the trial, prosecutors presented evidence and witnesses hoping to prove the cloth was forced into the baby's mouth.

The defense asked a medical expert if anything else could have caused such a cut, such as giving a prescription medication to a child who is resisting.

"In 38 years of pediatrics prescribing amoxicillin probably thousands of times, I've never had a child suffer a lacerated (lip) from being given an antibiotic," Dr. Bruce McIntosh answered. "I've never personally seen that."

Leaving court on Wednesday, the baby's mother, Donneka Steadman, talked about the pain of losing her baby.

"I wish I had him back, but I know it's not going to happen," Steadman told Channel 4's Dan Leveton. "I feel like I wish I never would have left my son unattended. I wish I could have did something different, but I know I can't."

The defense reste its case on Thursday afternoon. Closing arguments and jury deliberation are scheduled for Friday..