Prosecutors may have trouble convicting the accused killer of Linda Stein because of the way police obtained her confession, the lawyer for Stein’s two daughters, Edward Hayes, said.

“I don’t think they have a sure thing on this confession,” Mr. Hayes told The New York Sun yesterday. “It was clearly manipulative for them to meet with her because she was still a suspect in their minds.”

Stein’s accused killer, Natavia Lowery, 26, confessed early Friday morning at a police precinct in Manhattan to bludgeoning the famed real estate agent to death with a piece of exercise equipment called a yoga stick, police officials said.

However, Ms. Lowery’s confession could be deemed inadmissible in Manhattan Criminal Court, several defense lawyers said.

Ms. Lowery, who was Stein’s personal assistant, first met with investigators October 31, the day after Stein’s body was discovered by her daughter Mandy Stein inside of her Fifth Avenue apartment. Ms. Lowery’s lawyer, Gilbert Parris, contends that he told investigators during that meeting not to question his client without his permission.

Detectives did not speak again with Ms. Lowery until Thursday afternoon, when she called to complain about reporters that were camped outside of her Brooklyn home. The lead investigators on the case, detectives Kevin Walla and Antonio Rivera, made plans to meet with her at Kellogg’s Diner in the Williamsburg section of Brooklyn.

After meeting at the diner, Ms. Lowery was taken to a precinct house on the Lower East Side of Manhattan, where she waived Miranda rights and confessed to the murder, police said.

Family members of Ms. Lowery have said she was coerced into the confession. An aunt, Julia Carrow, told the Daily News that Ms. Lowery was not permitted by police to call her lawyer or her mother.

“They wouldn’t let her call nobody and kept her in there all night,” Ms. Carrow told the Daily News. “Then they came out and said she confessed.”

A high-profile defense lawyer, Ronald Kuby, said police could have infringed on Ms. Lowery’s constitutional rights by not contacting her lawyer before questioning her.

“If the lawyer had said not to question her, and the police took her into custody without contacting him, then every statement she made is inadmissible,” he said.

The police have argued that the interrogation of Ms. Lowery was justified because she reached out to the detectives.

“She called detectives herself and then answered their questions voluntarily,” the head spokesman for the police department, Deputy Commissioner Paul Browne, said.

Ms. Lowery’s confession was videotaped, police said. She told investigators that she became enraged and killed Stein after the victim verbally abused her and blew marijuana smoke in her face, police said.

While Ms. Lowery told investigators she beat Stein to death with a yoga stick, the murder weapon has not been found. Stein’s yoga instructor, Patricia Smith, said Stein did not own a yoga stick.

On the day of the murder, Ms. Lowery was recorded on security cameras leaving Stein’s apartment with a large bag, police said. Police also said she made several calls from Stein’s house that day.

Several people close to Stein said that while abrasive, they couldn’t believe Stein would blow smoke in anyone’s face.

Ms. Smith, who said she saw the two interact three times a week, said it appeared that Stein truly liked Ms. Lowery, and that the two had a good working relationship.

“Linda would always compliment her,” she said. “I never saw anything negative.”

Ms. Lowery was arraigned on Friday afternoon and is being held without bail on charges of second-degree murder. Mr. Parris, who yesterday said he is not commenting on the case, entered an innocent plea for his client.