When Kiheem Taylor was charged with kidnapping two teenagers at a Timonium light-rail station and raping one of them, prosecutors struggled with an all-too common problem — they didn't have enough solid evidence.

But Taylor gave prosecutors a break when he made phone calls from the Baltimore County Detention Center. Just months earlier, authorities had begun recording inmates' phone calls, and Taylor implicated himself while talking to an ex-girlfriend. Judge Robert N. Dugan said at the time that the call was "overwhelming, damning evidence of [Taylor's] guilt."

The 2008 case was the first time that Baltimore County prosecutors used a taped phone call from the detention center in a case, but the practice has been increasingly used across Maryland and the nation — including in the high-profile Trayvon Martin case. Though prosecutors say the evidence is crucial in otherwise difficult cases, defense attorneys complain that such monitoring is unfair to their clients.

William B. Buie III, who represented a teen in a recent murder case that relied on recorded prison calls, said he's concerned such calls give government unrestricted power to monitor incarcerated individuals who have not yet been convicted. But such calls are "playing a major part of criminal cases," he said.

Prosecutors have been monitoring calls for years, but improved — and increasingly affordable — technology has made it easier to record the calls, evaluate them and present them in court.

"It's definitely a common practice," said Steven Jansen, vice president of the National Association of Prosecuting Attorneys. "It can be great evidence."

It's no secret that the calls are monitored, he said, adding that some facilities even post signs next to phones. In Maryland, defendants are warned that their conversations are being recorded with a prompt each time they pick up receiver; officials can track them without seeking a judge's approval.

But despite the warning at each call, defense attorney Jerry Tarud said, "The problem is, when these inmates are in jail, they tend to get isolated. Their anxiety sets in."

For defense attorneys, the calls can be opportunities for their clients to unknowingly undermine their arguments, including in the Martin case in Florida. George Zimmerman, accused of killing the teen, had his original $150,000 bond revoked after authorities heard him discussing additional finances with his wife on a recorded line.

"The jail phone calls tend to be the nails going in the coffin," Tarud said. It's an increasing problem."

In a city shooting trial last year, Tarud's client, Donte Anderson, was convicted of first-degree assault after prosecutors pulled incriminating calls from jail.

In one call, prosecutors said, Anderson told an acquaintance about hiding the gun, in what they believe was coded language.

"Man … I can't event tell you where's it at right now cuz, he won't be able to get to it," Anderson said, according to court documents.

Dijon McClurkin, another defendant who was also convicted in the case, was allegedly also recorded telling an acquaintance to put pressure on the victim, who survived.

"You need to tell him that we ain't do nothing, yeah man, those [expletive] ain't do nothing, that's what he needs to say, [expletive] ain't do nothing, they are jammed up for no reason," McClurkin said in a recorded call, according to court papers.

In addition to monitoring phone calls, law enforcement officials point out that detention facilities monitor mail and keep records of who visits. Inmates are also subjected to searches inside of their cells.

There, each inmate can choose up to 10 contacts; they can only call people on that list, according to the state Department of Public Safety And Correctional Services.

The Baltimore County Detention Center began recording all inmates' calls in July 2008, one of the last jurisdictions in the state to adopt the technology. State's Attorney Shellenberger had suggested the idea to the county police chief and the jail's warden shortly after he took office in 2007.

The system was aimed at curbing contraband, gang violence and witness intimidation. Officials also hoped to prevent prisoners from ordering crime from behind bars.

Detention center staff, along with police and prosecutors, have access to phones in order to monitor for any potential problems within the facility. They also have the ability to block inmates from calling certain numbers if there are issues of witness intimidation or gangs.