Mehul Shah and Kalpesh Jani, employees of CMS Securitas Ltd told police after their arrest on Wednesday, that they did not have any money with them, as they had invested them in the stock market to earn some profit.

On Thursday, a day after the duo's arrest, the police went on an inspection drive checking security at ATMs around the city, while private banks and security agencies indicated the need for a major security overhaul.

Deepak Jani from CMS Securitas Ltd said they have beefed up security measures and enhanced more stringent audit checks. "We have incorporated some measures that we would not like to mention now. We are still working with the police to determine how they managed to steal the money," said Jani.

He said that the screening process for all employees has been strengthened after this incident.

Deputy Commissioner of Police (DCP) B K Shrimali said the theft had scared several private banks, which were now wary of the internal security mechanism for monitoring cash at ATMs. "The banks would be worried as any breakdown in the cash monitoring system is serious, but we will have more information after properly questioning the accused," Shrimali said.

Sources in the police said that that heist could involve bank personnel as well.