Despite the Department of Homeland Security's $945 million investment in radios for its border patrol agents, spotty coverage and inadequate training still hinders the agency's attempts to secure the southwestern border.

Some agents even told congressional investigators that radio communications worsened after DHS updated the system, according to a Government Accountability Office report.

Other border patrol agents reported experiencing "communications bleed" with the new radios, which happens when outsiders are able to listen in on conversations.

After building additional towers and installing new radios in Yuma, Tucson, the Rio Grande Valley and El Paso, DHS realized that approach was too expensive and time-consuming and instead focused on converting its analog systems to digital in five remaining sectors of the southwestern border that stretches from Texas west to California.

The Border Patrol has made no efforts "to determine whether the systems are working as intended" since upgrading equipment in those four of the nine sectors that span the southwestern border.

Although the agency's own policies mandate testing of new systems, patrol agents conducted "limited" testing only in the Rio Grande Valley. They declined to do so in Yuma, Tucson and El Paso, citing "changing agency priorities."

Because of the difficulty of connecting with officers from other agencies using their radios, Border Patrol agents "missed apprehensions of subjects," the watchdog found.

Most of the agents and immigration enforcement officers interviewed by the accountability office said they had been "involved in an incident in which a communications challenge jeopardized their safety."

This often occurred when agents had to chase a suspect without the ability to call for back-up on their radios.

A common way agents address that persistent challenge is to station an officer with other agencies, such as Immigration and Customs Enforcement, so he or she can relay what is said on Border Patrol radio frequencies to other agents, a practice the watchdog deemed "an inefficient use of agency resources."

Sen. Tom Carper, D-Del., noted in a hearing Tuesday that Customs and Border Patrol has more than doubled in size since 2003.

"We have constructed more than 600 miles of new fencing, and deployed sophisticated cameras, sensors, and radars across much of our border with Mexico," Carper said. "Today, we are deploying drones and aerostats high in the sky, as well as fixed and mobile observation towers, providing situational awareness for our agents on the ground."

Border Patrol drones have drained $360 million from the Homeland Security budget while meeting few surveillance expectations, the Washington Examiner reported in January.

Despite the integration of new technology into patrol procedures, officials are still struggling to find communications systems — including radios — that allow its agents to communicate with officers at other federal, state and local agencies more than a decade after the 9/11 Commission highlighted the agency's need to develop such capabilities.

Criminal activity along the southern border has also mushroomed in recent years. Transnational criminal groups such as Mexican drug cartels work to exploit border patrol's weaknesses in their efforts to smuggle illicit substances into the U.S.

"An extensive system of scouts armed with radios, solar-powered radio repeaters, cellular phones and weapons situated on high points along drug trafficking routes are vital to the smuggling groups," said Elizabeth Kempshall, executive director of the Office of National Drug Control Policy's Arizona High Intensity Drug Trafficking Area, at the Senate hearing Tuesday.

Kempshall said such scouts allow criminal groups to keep tabs on law enforcement while shepherding their drug cargo around border patrol operations. She touted the importance of interagency cooperation in cracking down on transnational crime.

While most border patrol and immigration enforcement agents were given basic radio training, officials told the Government Accountability Office they felt more education could help them put the technology to better use.

Some agents reported receiving no training at all. Officials said they "receive intensive firearm training and must demonstrate proficiency with their firearms on a quarterly basis, yet they use their radios far more frequently than they do their firearms and are not required to demonstrate proficiency in using their radios."

The watchdog discovered "some local managers may determine that training is not a priority."

Installing the combination of new and refurbished radio systems across different regions along the border won't be completed until 2016, although border patrol agents said they anticipate delays could push some upgrades back to 2018.

Go here to read the full Government Accountability Office report.