Four persons arrested in connection with an attack on the Chief Executive Officer of the Tamale Teaching Hospital (TTH) on Monday have been released, Joy News sources say.

Police in the Northern Region Capital, Tamale, explain they are unable to establish any evidence that the four suspects took part in the forced entry into Dr David Akolbila’s office.

Although TTH authorities were called in to identify the suspects and establish that they were part of the thugs that besieged the CEO’s office, they could not do so, the sources reveal Wednesday evening.

Police, meanwhile, say investigations are ongoing.

Related: Tamale lawlessness: Innocent patients cannot pay for govt's inaction- Haruna Iddrisu

The attackers accused the hospital's CEO of corruption and mismanagement but provided no evidence to back the allegation.

They walked into the offices of Dr David Akolbila, walked him and his staff out and locked the offices.

In protest, the health workers of the hospital also declared a strike.

The workers say they no longer feel safe in the hospital after Monday's incident.

The attackers are believed to be members of a vigilante group affiliated to the governing New Patriotic Party (NPP).