He also did not rule out himself questioning the prime accused, Jolly.
After lengthy meetings with the police probe team investigating the murder trail in the family of the accused serial killer, Behra said: "This is a challenging case. I have come here, as this is an important case.
"Six murders have taken place and hence there are six separate cases.
"The challenge in this case is that the first murder took place 17 years back and the last one took place three years back and hence collection of evidence is most crucial."
He spoke to the media, before heading into another brain storming session.
All the mysterious deaths took place in the family of retired government official Tom Thomas and all six dead bodies were exhumed last week for the further scientific investigations.
"Today we have constituted six different teams along with a supervision team and more people will now be inducted. It will include more forensic and legal experts.
"The other challenge is collection of evidences, the team here has been successful in detecting the crime," said Behra.
He also pointed out though that nothing is impossible for the investigators.
"There will now be several tests that has to take place and my job is to assist the team. At the moment the task of the probe team is to get maximum information from her.
"We are optimistic, there will be some traces left somewhere," added Behra.
The first in the family to die in 2002 was Jolly's mother-in-law Annamma, a retired teacher. She was followed by Jolly's father-in-law, Tom Thomas, in 2008. In 2011, their son and Jolly's husband, Roy Thomas, also died to be followed by the death of Roy's maternal uncle, Mathew, who died in 2014.
The two-year-old child of Sily, a relative by marriage, died the following year, while Sily passed away in 2016.
It was only on Friday that the police registered five more separate cases of murder.
It was on Thursday, a lower court here remanded Jolly and her two accomplices M.S. Mathew, who procured cyanide, and jewellery store worker Praju Kumar to six-day police custody for the murder of Jolly's husband Roy Thomas.
On Friday, all the three accused were taken to six places as part of evidence collection. It was part of investigation into the death of Jolly's first husband Roy Thomas.
( With inputs from IANS )