Marta S. Goldstein leans in to hear what the judge is saying during private conferences at the bench, sometimes pulls up a chair near a soft-spoken witness who is testifying, and strides across the courtroom to the jury box to catch everything the attorneys say.

All the while, she whispers into a tiny microphone, as if she is a play-by-play commentator on a golf course.

Goldstein is one of several courtroom interpreters with the daunting task of seamlessly changing from English into Spanish every word in the Baltimore Circuit Court trial of two illegal Mexican immigrants accused of killing three children. The defendants listen to the interpreters through headsets.

Policarpio Espinoza, 23, and Adan Canela, 18, are charged with three counts of first-degree murder and conspiracy in the May 27, 2004, deaths of their young relatives in Northwest Baltimore. Under Maryland law, the men, who speak little English, are entitled to hear their criminal court proceedings in their native tongue.

"There are no words to convey the importance of what we do," says Goldstein, who with 26 years of experience is considered the state's senior courtroom interpreter. She trained many of her colleagues and helped write state policies on how interpreters fit in the courtroom.

They handle a variety of criminal and civil cases, from child custody disputes to murder.

"Based on what we say, a mother could lose her children," she says. "Someone who should go to jail may not. ... One word we utter incorrectly could cause a mistrial."

The interpreters take an oath to accurately interpret the court proceedings.

Throughout Maryland, there are 111 certified interpreters who can work in any district, circuit or appeals court, according to the state Administrative Office of the Courts.

Almost all of them are Spanish speakers. The state also certifies interpreters in Vietnamese, Korean, Russian, Cantonese and American Sign Language and will begin certifying in Arabic and Haitian next year.

The next level of certification is in the federal court system, which Goldstein says is extremely difficult to achieve. She says only about 800 of the 42,000 people who have taken the proficiency test become certified to interpret in federal courts.

State-certified court interpreters earn $50 per hour with a two-hour minimum, Goldstein says. Federally certified interpreters, such as Goldstein, earn a daily rate of $329.

The state Administrative Office of the Courts says no one keeps statistics on how many court cases require interpreters, but anecdotally, judges say they have needed those services more and more.

"Particularly in places like Prince George's, Montgomery, Howard and Anne Arundel [counties], there is a higher demand for courtroom interpreters," says Baltimore Circuit Judge Audrey J.S. Carrion, chairwoman of the statewide judiciary committee on interpreters. "It's a reflection of the change in diversity in our communities."

Courtroom interpreters must be so fluent in the languages they're translating that they have command of the vocabulary that lawyers, judges and expert witnesses use and the street vernacular that can come up during a criminal trial.

Goldstein was born in Colombia and grew up speaking Spanish and English.

The Espinoza-Canela trial is lengthy - it's in its fifth week of testimony - and complicated, with witnesses discussing subjects such as latent fingerprints and the science of DNA. Goldstein says Circuit Court Administrative Judge Marcella A. Holland asked her to help arrange for some of the most experienced interpreters for the high-profile trial.

Although the lawyers sometimes fire off questions at a furious pace, and the witnesses give long, convoluted or barely audible answers, the interpreters rarely interrupt the trial's flow. Often, they're breathless at the end of the day.

There are two interpreters in the courtroom. One speaks into the microphone while the other sits attentively. The interpreters have developed a nonverbal language, too. When Goldstein doesn't know a word, she only has to glance at her colleague, who will rush forward to whisper it into her ear.