In a new twist in the Nitish Katara murder case, a key witness alleged on Thursday that he was poisoned by some persons but police and doctors denied his claim.

Ajay Katara, no relative of the victim, got himself admitted to a private nursing home on Thursday afternoon claiming that he was fed some poisonous substance late Wednesday night by five people after calling him to nearby Mohan Nagar.

He said he knew the names of two of the five persons but mysteriously did not inform police.

He argued that it would have served no purpose and alleged he feared a threat to his life from UP politician D P Yadav, whose son Vikas and nephew Vishal are the prime accused.

While Ajay Katara was discharged in the evening, police rubbished his claim, saying it could have been a simple case of food poisoning.

An investigation has been ordered into the incident.

"Doctors have told us that no trace of poison was found on him. But it could be a case of food-poisoning," Superintendent of Police (Ghaziabad City) Vijay Bhushan told PTI.

Rajesh Bhajaria, the doctor of the nursing home who attended on him, also said that 'it is a clear case of food poisoning and there are no symptom of poisoning'.

He said Ajay refused to cooperate with doctors when they tried to wash his stomach.

"Neither Ajay nor anyone from his family filed an FIR in the case", Bhushan said.

Ajay Katara is a prime witness in the murder case as, according to prosecution, he had seen Nitish going in a car along with Vikas and Vishal before being murdered in February, 2002. He has already been provided security.