The mother of a young British aristocrat killed by Kenyan police nearly a decade ago has spoken of her disappointment after the officers convicted of his death were told that they would all be freed within 10 years.

In a potentially defining moment for the country’s notoriously brutal services, a Kenyan judge said on Monday that he had no doubt that Alexander Monson, heir to Monson baronetcy in Lincolnshire, died after police “brutally tortured” him.

Although Justice Erick Ogola said it was clear that at least one the police officers standing before the dock had murdered Mr Monson, who was 28 at the time of his death, it was impossible to tell who had carried out the killing.

Accusing all four of creating a “wall of silence” to cover up the crime, he found the four officers—Naftali Chege, Charles Munyiri, Baraka Bulima and John Pamba— guilty of manslaughter instead.

He handed down sentences of between nine and 15 years, but suspended up to half of each sentence.

As a result, Police Sgt Chege, seen by Mr Monson’s family as being the chief culprit, will serve 10 years, while Constable Bulima will serve just four. The fourth defendant, Constable Pamba was told he would not have to begin his sentence for a year due until he had healed from a leg injury.

Speaking after the sentences were handed down, Hilary Martin, Mr Monson’s mother, suggested that the verdicts had amounted to less than the family had hoped for.

“As Alexander’s mother I am feeling very emotional, I cannot disagree with the judge who is an expert in law while I am not but as a mother it seems a very poor exchange for 10 years of arduous work for a sentence of half that.”

Lord Monson, however, struck a more upbeat note, saying that the convictions represented an important moment for the many Kenyans whose children have also been killed by the police.

“It’s a good day, not necessarily for us as we won’t get Alexander back, but for other Kenyans who have been in similar situations,” he said.

“I’m not sure of the verdict. I think it could have been stronger but I am happy that they are going to jail and they are going find that it is not a very nice place. They are certainly unlikely to receive a very good reception from other inmates.”

As Nicholas Monson, the 12th Baron Monson, and his former wife Hilary looked on, Justice Ogola said: “How four seasoned police officers could allow the death of a young man under their watch is the tragedy of this case.”