Castro's indictment references a network of Cuban spies. Who were they?

Members of The Wasp Network became national heroes in Cuba after their capture. (Reuters: Desmond Boylan)

In the early hours of September 12, 1998, FBI agents crashed through the doors of several Miami homes and arrested 10 people.

Prosecutors alleged they made up part of a Cuban spy ring codenamed La Red Avispa, which translates to The Wasp Network.

While their criminal trials were long-running and controversial in the early 2000s, the world had largely moved on from their story.

The move is the latest escalation in Washington's pressure campaign against the island's communist government.

That was, until the US government charged Raúl Castro earlier this month with four counts of murder.

The indictment of the former Cuban president relates to a 1996 incident in which two planes operated by a group of Cuban exiles known as Brothers to the Rescue were shot down.

It alleges that The Wasp Network fed Castro intelligence to facilitate the attack.

But the arrest of network members revealed they never got hold of any state secrets.

Tensions between the US and Cuba were high in the latter half of the 20th century, a matter Cuba felt Brothers to the Rescue was exacerbating during the 1990s.

People were increasingly fleeing the island nation on makeshift rafts, in the hopes of landing in Florida.

Many refugees did not survive the perilous journey due to dehydration, starvation, hypothermia and drownings.

In response, Brothers to the Rescue dropped supplies from small planes to the fleeing Cubans and on several occasions entered Cuba's airspace to drop anti-government leaflets over Havana.

Cuba considered the actions of Brothers to the Rescue a provocation and warned aircraft violating its airspace risked being shot down, a threat it ultimately delivered on in 1996.

A Brothers to the Rescue plane flying over The Democracy Movement flotilla at the 12-mile limit north of Havana, Cuba in 1999. (AP: Alan Diaz)

Amid these tensions, Cuba deployed The Wasp Network to the US to gather intelligence on anti-Cuban activities.

Perennially broke and hapless in matters of health and romance, the spies apparently had little time for obtaining state secrets.

Details of their lives in Miami emerged from 1,400 pages of records confiscated by the FBI from encrypted computer discs.

They memorised fake life stories, took on day jobs and frequently agonised over threats of detection.

The United States has indicted former Cuban president Raúl Castro on murder charges stemming from 1996.

The spies spent an increasing share of their time supplementing the meagre stipen