Two men armed with weapons including a samurai sword and equipped with body bags and gaffer tape were arrested as they plotted to rob and murder the soul singer and actor Joss Stone, a jury has heard .

The pair drove from Manchester to Devon, where Stone lives, but were spotted by concerned neighbours who dialled 999. When police searched the men's car and home they found a note describing Stone as a "she-devil in flesh" and others suggesting that they had considered decapitating her and finding a river to dump her body in.

The notes also made references to Stone's connections to the monarchy – royals have attended her concerts and she was invited to Prince William's wedding.

Simon Morgan, prosecuting, said the men – Kevin Liverpool, 35, and Junior Bradshaw, 32 – may have targeted Stone for financial reasons or even because they disliked her royal links, but he added: "Their motive may never be clearly established – we may never know."

Morgan told the jury at Exeter crown court that Stone – real name Jocelyn Eve Stoker – was an "extremely successful" singer and songwriter.

In 2008 she moved to a house in a village a few miles from Culmstock in Devon. Morgan said that her life was "nomadic" but at the time of the men's arrest was at home.

Morgan claimed that Liverpool and Bradshaw, along with others who have not been traced, had decided to find Stone, rob her and kill her.

According to the prosecution, Liverpool used a computer at his local library to research various artists before fastening on Stone. "He settled on Joss Stone," said Morgan. "He found out quite a bit about her. He knew she had money. He obviously decided to concentrate on her."

Morgan said the men had printouts of maps showing Stone's house and wrote about her home in notes. Two weeks before they were arrested there was a reconnaissance trip to the village where Stone lived, it was claimed. At that time a neighbour saw a red car driving slowly past Stone's home.

In June 2011 the men allegedly armed themselves with the sword along with hammers, a metal spike and a knife. They were also equipped with balaclavas, gloves, body bags, gaffer tape, maps and a roll of plastic bags.

Morgan said: "The crown says that with this arsenal of weapons, it is obvious they were intent upon serious violence. The intended target was Joss Stone. They had decided upon this action some time before and this was the time to put it into effect."

Their red Fiat Punto car was picked up by an automatic registration plate recognition system on the M6 in Cheshire at 2.35am. Two hours later they filled up with petrol on the M5 in Gloucestershire and drove off without paying for it, Morgan said.

As they left the service station, the car crashed into metal railings and a digger. The front of the vehicle was badly damaged and Gloucestershire police attended. Officers said they would report Bradshaw for driving without insurance and other offences. Police did not believe that the vehicle could be moved, so left the scene and did not search the car.

Morgan said the men were not put off and drove on to Devon. They got lost and showed a postman a picture of Stone and one of the men asked him where she lived, the jury was told. The postman told them he did not know.

Later three local women saw the car. They thought the occupants were "agitated and behaving abnormally" and phoned the police. A patrol car followed the Fiat, then stopped it, at which point the weapons and equipment were found.

When the men's flat in Longsight, Manchester, was searched, police also discovered a pistol, crossbow and a BB gun. Notes found included the message: "Joscelyn (sic) Stoker … RIP for ever" and "I don't kill just for dollars, only for good cause or reason".

One mentioned decapitation and another read: "Once Jocelyn's dead … find a river to dump her."

Morgan said one note also described the Queen as a "she-devil" and added: "But she likes Joss Stone. Invited to Will's wedding by Queen. Where's the sense in that?"

Morgan told the court: "The items in their possession, the trips to the area, the fact that the intended victim was at home, the notes and maps all point to a determined effort on the part of the defendants to carry out the plan they had hatched some time before."

The men deny conspiring to murder Stone and also plead not guilty to conspiring to cause her grievous bodily harm or conspiring to rob her. The trial continues.