Maryland Transportation Authority Police are preparing murder charges against a West Baltimore man who police believe threw his 3-year-old son off the Key Bridge into the Patapsco River on Sunday.

After more than two days of searching, police had not recovered the boy's body. But police said phone calls from relatives and statements from witnesses on the bridge Sunday night led them to believe that Turner Jordon Nelson had been thrown into the water.

The boy's father, Stephen Todd Nelson, 37, of the 2900 block of Walbrook Ave., was in critical condition in an induced coma at University of Maryland Medical Center after ingesting household cleansers Sunday night in an apparent suicide attempt at his home, police said.

According to police sources, Stephen Nelson's mother called 911 several times Sunday night, saying that her son had thrown her grandson, still in his car seat, off the Key Bridge. She told police that her son and the boy's mother, Natisha Johnson of Gwynn Oak, have had domestic problems.

A calm but distressed Johnson said in a phone interview last night that she had no idea that Nelson was capable of harming their child.

She described their current relationship as average and said they usually did not talk unless it involved Turner. Computerized court records indicate that she and Nelson had been fighting over custody and visitation issues for the past two years in Baltimore County Circuit Court. The case was still active, according to the records.

Johnson said police told her not to publicly discuss the specifics of her last conversation with Nelson. But she said that in an earlier conversation after he had picked up their son, he threatened to throw him from a bridge.

"He was a good family man," Johnson said. "I can't even imagine him doing this. He was a normal guy."

Johnson said she believes Turner might be alive.

"I'm still hoping for the best, still praying that this is a nightmare and that he did not do what he actually said he did. And that he just took my son somewhere else," Johnson said.

Irene Johnson, Turner's maternal grandmother, said she took care of him daily at the house on Ransome Drive in Gwynn Oak that she shares with her daughter, the boy and two other relatives.

She described Turner as smart and lovable, a joy to be around.

She said she, too, could not believe that Nelson would harm Turner.

"It's something I personally thought he would never do. He really seemed to care about this baby a lot. It just broke my heart," she said. "But he called my daughter and told her he was going to do it."

Irene Johnson said she had no idea why Nelson made the threat.

"He never even showed any kind of violence toward the baby," she said. "And Turner really loved him. When he saw his dad, his face lit up."

Irene Johnson said while Nelson argued with her daughter during their long-running custody dispute, he never physically abused her or the child.

On Sunday night, several state and local police agencies - as well as the U.S. Coast Guard and the state Department of Natural Resources - began a water, land and air search of the Patapsco River for the child, said Cpl. Jonathan Green, an MdTA police spokesman.

The 2.4-mile Key Bridge links the Baltimore Beltway across the Patapsco and is 180 feet from the water at its highest point, according to police sources; the river's depth in the vicinity is at least 40 feet.

Green said information from at least one witness as well as the recovery of Nelson's 2001 Mitsubishi Galant and other facts regarding the missing child led his agency to seek the murder charges. He did not know when the charges would be filed.

A person who did not identify himself at Nelson's Walbrook Avenue home last night declined to comment.

richard.irwin@baltsun.com brent.jones@baltsun.com