Four men have been jailed for their part in a failed plot to break a contract killer out of prison by hiring a helicopter.

The plan to spring Benaouf A. from jail in Roermond last October foundered when the helicopter rental firm became suspicious of the men’s intentions and contacted police, NRC reported.

The sentences handed down by the district court in Amsterdam of between two years and 30 months were lower than the three to nine years demanded by the prosecution, mainly because the plot had been thwarted at an early stage. Five other defendants were acquitted.

Police who raided the men’s homes found a handgun, automatic weapons and ammunition, along with rockets, jerrycans and home-made caltrops, spiked weapons shaped like crows’ feet that are used to puncture vehicle tyres.

Despite the relatively light sentences, the court said a ‘very serious and dangerous situation’ had been prevented, adding that the gang showed a ‘total lack of respect for the justice system.’

A. was serving a 12-year sentence for a murder committed in Antwerp in 2012 during the so-called ‘Mocro Wars’ between rival drugs gangs.