The frantic voice message to an inmate in Colombia’s notorious La Picota prison came days before powerful former President Álvaro Uribe was up against a court deadline to submit witness testimony in a potentially damaging case against him.

“There’s a big man who wants to talk,” Carlos Eduardo López, a tireless Uribe devotee, told the former paramilitary serving a four-decade sentence.

Juan Guillermo Monsalve asked for details. In a series of WhatsApp audios, López explained that Uribe’s political allies wanted him to help their cause by submitting a video in which he backtracks from previous statements alleging the politician had ties to right-wing paramilitaries.

The Supreme Court had just opened an investigation into allegations that Uribe had engaged in witness tampering and his supporters were eager to get it closed. If Monsalve could testify that he'd been pressured by an opposition lawmaker into making false assertions against Uribe, he could help spare one of Colombia's most popular if polemical leaders a possibly ruinous legal headache.

The audios are among a trove of legally intercepted calls, covert recordings and witness testimony that make up the backbone of a monumental Supreme Court investigation into Uribe, whose house arrest order last week rocked the political establishment and divided the nation.