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ABC's '20/20' investigates murders committed by felons wearing monitoring devices

In many cases, the ankle devices triggered alerts before murders were committed but authorities took no action

American prison systems are, more often than not, notoriously overcrowded and understaffed. The country has the highest incarceration rate on the planet and monitoring devices such as ankle bracelets often enhance public safety, reduce costs of running these prisons, and provide social benefits.

However, a nationwide investigation has found that, since 2012, at least 50 murders have been allegedly committed by those who, at the time, were under orders to wear electronically monitored ankle bracelets.

ABC's '20/20,' which aired this Friday, May 25, takes an in depth look at how those responsible for tracking these devices are failing to do so. 

In some of these cases, the authorities supposedly failed to appropriately monitor the people wearing these bracelets or respond to alerts set off by the electronic devices. One such case involved the murder of Alex Zaldivar in Orange County, Florida.

Zaldivar was shot and killed by a man named Bessman Okafor. Okafor broke into the home where Zaldivar lived with his roommates, Brienna and Remington Campos, and shot all three, killing him in the process. Okafor was wearing an ankle bracelet after he was ordered to do so following a robbery at the same home earlier in the year. Two of the roommates were even scheduled to testify against him in connection with the crime the very next day.

Another such unfortunate incident involved the death of Lori Bresnahan in Syracuse, New York. Bresnahan was murdered by David Renz, who was supposed to be wearing an ankle bracelet while awaiting trial for possession of violent child pornography.

In both the above cases, the ankle devices triggered alerts before the murders were committed but authorities took no action.

In '20/20' Brian Ross of ABC News investigate the crimes and the failures of ankle bracelet-monitoring. The show features interviews with Rafael Zaldivar, the father of Alex, and Bill Creggwill , who was the first to arrive on the scene of the murder of Bresnahan.