Officers are continuing to probe the deaths of Tracey Arden, Arnold Lancaster and Derek Weaver who all died after being given contaminated saline. Assistant Chief Constable Terry Sweeney, of Greater Manchester Police, said: "This is and always has been a search for the truth. About 650 people have already been interviewed, including doctors, nurses and pharmacy staff over the scandal at Stepping Hill hospital. Stockport NHS Foundation Trust, which runs the hospital, said it was "appalled." Chief executive Chris Burke said: "We are aware that Greater Manchester Police has arrested a 46-year-old man on suspicion of tampering with prescription charts. Because of highly experienced doctors and nurses immediately spotting the changes on prescription charts, no patient has been harmed. The police were called as soon as the prescription chart changes were discovered via our routine good practice. We are appalled by the malicious intent of this act, but thanks to the skill and experience of our staff it was spotted and reported immediately, and most importantly we ensured no patient suffered any ill-effects. This criminal act does not reflect on the good care provided by dedicated and committed staff and the effective working practices in our hospital. The safety of our patients remains our highest priority. As no charge has been made, it is important to note that police are continuing with their inquiries. We continue to support the police in this ongoing investigation.