A stalker threw rocks through a man's window and sent notes threatening to harm his children.
Neil Whittaker was hired to carry out a campaign of fear against the man at his home in Leeds in order to settle a drug debt.
A court heard Whittaker threw a rock through the man's home in Guiseley, Leeds, and sent a note which read: "Your children are next".
The 37-year-old also made threatening phone calls to the same man, telling him: "You think the police are going to to stop me? I know where you live.
"If I don't have you I will get your children.
"If I don't get your children I will have your family."
Whittaker was jailed for 21 months after pleading guilty to an offence of stalking.
A second defendant, Ben Hales, 31, was jailed for four months for harassment after his fingerprints were found on a note posted through the victim's letterbox.
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Howard Shaw, prosecuting, said the man who was targeted by the defendants had been a victim of an armed robbery in 2015.
Two other men were subsequently convicted and jailed over the robbery offence.
Mr Shaw said the victim moved to a different area of Leeds after the robbery.
Whittaker targeted the man in his new home in June 2017.
The prosecutor said he returned home one day to find find a note on his front door which read: "You can't hide."
Another note - which was found to contain Hales's fingerprints - was posted through the letterbox.
It read: "I am gonna be your regular postman. Means you will see me on a regular basis."
The prosecutor said the man found the note extremely distressing and contacted police.
Police enquiries revealed that a hire car linked to Whittaker had been parked close to the man's home earlier in the day.
CCTV footage was also obtained of Whittaker jumping over the victim's garden wall and getting into the car.
He then drove the Volkswagen Golf back to his home in Nottingham.
Whittaker, of Chewton Street, Nottingham, was seen on camera driving on the M1 back to Leeds the next morning.
At 6.30am the victim was asleep on his sofa in the living room when two rocks were thrown through his windows.
A note next to the rock read: "Your children are next."
Evidence was also obtained that Whittaker made threatening phone calls to the man the next day.
Dale Harris, for Whittaker, said the offence was unusual as his client did not know the victim and has never met him.
Mr Harris said Whittaker agreed to carry out the offence after he got into a debt with drug dealers.
He said: "It is akin to witness intimidation.
"I am not sure that makes it any better or any worse. It is an explanation and it is the only credible, truthful explanation.
"This is an unpleasant and, quite frankly, a nasty scenario. It was his way of repaying the debt.
"He doesn't know what the background was. He wasn't involved in the offence which (the victim) was involved in 2015."
Joe Culley, for Hales, of Kentwood Road, Nottingham, said his client's explanation for committing the offence was "somewhat similar" to Whittaker's.
Jailing the pair, Deputy Judge Robert Moore said: "It was a serious threat against a vulnerable victim."