U.S. Marshals monitor activity outside the Martin Luther King, Jr. Federal Courthouse before opening statements are heard in the "Bridgegate" trial on Sep. 19, 2016 in Newark, New Jersey. (Mark Makela/Getty Images)

More than 1,400 law enforcement officers with the U.S. Marshals Service are wearing expired body armor, despite months of internal warnings, according to documents obtained by the Senate Judiciary Committee.

Ballistic vests have become a staple of law enforcement work, but the equipment can wear out or age so much that it becomes less effective at stopping bullets.

A senior employee of the U.S. Marshals recently provided documents to the Judiciary Committee showing that many of the agency’s 3,900 operational employees have body armor with expiration dates in 2016 and 2017. The employee told committee staff he had been pressing the marshals for months to update the vests without much response.

The committee’s chairman, Sen. Charles E. Grassley (R-Iowa), is now pressing David Harlow, the head of the agency, to explain why so many of his employees have outdated body armor, and why he had previously testified to Congress that he was not aware of such problems.

“More than 1,400 operational U.S. Marshals Service employees reportedly were wearing expired soft body armor at the end of June,’’ Grassley wrote this week to Harlow.

(National Institute of Justice)

The Marshals Service guards courthouses, judges and witnesses, but it is best known as a fugitive-hunting agency. Apprehending fugitives, which often involve knocking down doors and searching houses, is particularly dangerous, and ballistic vests are essential gear for that work.

“Body armor” is something of a misnomer, because Kevlar and other products are tightly woven fiber panels designed to stop bullets from handguns. But those panels — made to go inside cloth vests — come with expiration dates, typically five years. How a vest is worn and stored can also change the effective life of a ballistic vest.

Michelle Coghill, a spokeswoman for the marshals, said safety of their personnel “remains our agency’s primary concern as we routinely pursue the most dangerous fugitives in the nation.’’ She said the agency has replaced about 1,540 body armor vests through February and has funding to replace all expired vests by the end of September.

James Gagliano, a former FBI supervisor, said it’s important to keep up-to-date equipment but that how a vest is used and stored can be a bigger factor than age in determining its effectiveness.

“The two biggest things that degrade them are exposure to water and direct sunlight,’’ Gagliano said. “Letting them sit in the trunk of a hot vehicle also isn’t good.’’

Gagliano compared expiration dates on ballistic vests to expiration dates on medicine, adding “you’d rather err on the side of turning them in too early than turning them in too late.’’

Federal agencies tend to be conscientious about replacing older vests, Gagliano said, but local law enforcement agencies sometimes try to put off such purchases to save money. “It’s not going to become a cause celebre until the first cop is killed by a round that wasn’t stopped and should have been stopped,’’ he said.

Depending on the amount of wear and tear on a ballistic vest, expired body armor can fail at a higher rate. Tests have shown that tests on five-year-old soft body armor “resulted in 11 penetrations out of 84 shots taken,’’ according to Grassley’s letter, which says the agency has been replacing some, but not all, parts of their deputies’ body armor.

Grassley said he was also concerned because the issue was raised at an April hearing.

“When a member of the House subcommittee asked you about expired equipment on April 26, you stated you were not aware of it,’’ Grassley wrote in his letter to Harlow. The senator added that the Marshals Service budget “suggests the agency knowingly underfunded the plan, resulting in expired armor that the agency knew had a significant failure rate.’’

The issue has simmered behind closed doors since March, when a senior U.S. Marshals employee first provided information about the ballistic vests to Grassley’s committee. The employee was removed from his acting duties and given different responsibilities, prompting Grassley to complain to the agency that “this type of behavior is Retaliation 101, and it interferes with congressional oversight activities.’’

Grassley is also demanding answers about concerns raised inside the Marshals Service that the agency’s fugitive-apprehension training program is inconsistent, leading to greater risks, particularly when deputies from different regions work together.

In a separate letter, Grassley wrote that the training program apparently “has not been implemented as designed, un-vetted instructors are not teaching the standard training, deputies are learning disparate techniques and there is little oversight of what is actually taught and deployed in high risk fugitive operations. The result is more risk, not less.’’

Grassley said the apparent lapses may have contributed to the 2015 death of a deputy marshal in a high-risk fugitive apprehension operation in Baton Rouge.

Coghill, the spokeswoman, said the agency’s fugitive-hunters receive “comprehensive, state-of-the-art training to ensure our deputies can safety executive high risk fugitive operations,’’ and she said the agency conducts vigorous reviews of incidents in which deputies are killed.