Stephen T. Nelson and his girlfriend, Natisha Johnson, argued a lot. They fought about his tardiness, about whether to send their son to day care, about all the stuff she left behind when she moved out.

In the end, they fought long and hard over custody of 3-year-old Turner Jordan Nelson, a "happy little boy," his mother said, who loved to spell long words such as elephant and xylophone.

Police say they believe that Nelson, 37, threw the toddler off the Key Bridge into the frigid Patapsco River on Sunday night. Shortly afterward, Nelson tried to kill himself by drinking household cleansers, police said, and was taken to University of Maryland Medical Center in critical condition. He remained in an induced coma yesterday, and police said they plan to charge him with murder.

The boy's body had not been found by yesterday afternoon, and a search of the waters continued.

"I never thought that he would actually hurt his son," Johnson, 28, said yesterday in an interview around the dining-room table at her parents' home in Gwynn Oak. "I still don't think that he hurt T.J."

Speaking calmly and with little emotion, Johnson said she believes that her son will reappear. She said she was shocked by Nelson's apparent suicide attempt. She left him about three years ago, she said, because she no longer loved him and was intimidated by his drinking problem. She said she did not want her son growing up around that kind of behavior.

The couple met in 2000 and lived for a couple of years in Rock Hill, S.C., before moving back to their native Baltimore. They were together, she said, until six months or so after the birth of their son - whom they called T.J. - on Sept. 23, 2004.

She did not completely move out of his home on Janper Court in Baltimore County until she was granted custody of Turner in May 2006. Three weeks later, Nelson said in a criminal complaint, she struck him on the forehead with a blunt object.

Johnson had come "to remove the rest of her personal belongings," he said in the court document, and told him to dispose of whatever was left. "I told her that it was her stuff and she should throw it away," Nelson said. As she was leaving, "she hit me with a stick that is part of a coat rack," he said. "That's when I called 911."

Johnson was charged with second-degree assault but was found not guilty. A year later, in May 2007, she filed a domestic violence complaint against him and was granted a temporary protective order. She said there had been no violence but that he had "acted threatening" and she was afraid of him.

"He has left notes on my car, call me names when I don't do what he wants me to do," she wrote by hand in the court document.

Without explanation, she withdrew her complaint in a few days.

All along, the documents say, Nelson and Johnson had been sparring over their son, about who was best equipped to take care of him. Despite having established visitation rights, Nelson complained in February 2006 that he was being prevented from seeing his son on weekends. A month earlier, Johnson had requested full custody of Turner on the grounds that his father only saw the child "when it is convenient for him."

"My son is very close to me because he is with me the most," Johnson said in a court document.

By April 2007, Nelson, who had worked in a warehouse in Pasadena, often at night, was asking the court to amend the custody order so that the couple could have joint custody over the child. "My employment situation gives me more time to myself and my son," he wrote. "I would love to have my son with me as much as possible."

His ex-girlfriend opposed any change, saying Nelson was "not dependable."

"Mr. Nelson has on previous occasion threatened to use joint custody to keep our son away from me," she said in a filing.

Later, however, a mediator helped the couple agree to joint custody of Turner and "to share responsibility for all major decisions concerning him, such as those pertaining to medical care, religious upbringing and education," according to the agreement signed Oct. 5, 2007. They agreed also to return to the mediator if they arrived at an impasse.

Nelson had been married to another woman, Yvette J. Mundell, with whom he had a son, Bernard, born Sept. 19, 1994. Mundell filed for divorce on grounds of adultery Dec. 16, 2004, three months after the birth of Nelson's child with Johnson.

As the search for Turner persists, Chief Marcus Brown of the Maryland Transportation Authority Police said his agency is working with the city state's attorney's office on charges against the boy's father. Brown said he hopes Nelson will recover and explain what happened.

Brown said the transporation police received calls Sunday from motorists on the Key Bridge who reported that a man had parked his car on the span and was standing on a walkway. An officer was dispatched from the toll plaza and arrived on the scene within a few minutes of the report. The officer found nothing.

Within a few hours, police were searching the waters with Baltimore police, Maryland State Police and the Coast Guard, by boat and by helicopter.

Brown said officers dropped a buoy into the water and tracked the current. He said that contrary to earlier reports, the child was not thrown into the water strapped to his car seat, which was found inside Nelson's car.

As she patted a picture of her son in a photo album yesterday, Johnson was hopeful.

"That's my baby," she said. "I have a feeling he's coming home, because someone is going to do the right thing and give me back my baby."

nick.madigan@baltsun.com gus.sentementes@baltsun.com