Tonga's Police Commissioner says some people were reluctant to speak to police during their investigation into the Princess Ashika disaster.
Four men and the Shipping Corporation of Polynesia have been found guilty of charges including manslaughter by negligence in relation to the sinking in 2009.
The corporation's former chief executive John Jonesse, captain Maka Tuputupu, first mate Semisi Pomale, and a former transport ministry director, Viliami Tu'ipulotu, have been remanded in custody for sentencing on Monday.
Police Commissioner Chris Kelley says there is insufficient evidence of gross negligence to charge anyone else.
He says some of those interviewed found it difficult to answer questions.
"One of the issues there of course is because the Commission of Inquiry ran parallel to the police inquiry, I think that in some cases people were probably reluctant to discuss with the police, reluctant to say too much, but that's always a matter for the individual I suppose. It's their right whether they answer questions or not."
Chris Kelley says police did receive cooperation from government ministers and departments.
But the sister of a woman who died in Tonga's Ashika disaster says the government was at fault and ministers should be charged.
Tasha Sulaki's sister died in the sinking, along with her sister's husband and two of their children.
She says her mother cried when she heard the verdict, but they believe the government is to blame.
We know that's the government's fault because they know that the boat is not good enough to bring here to Tonga, because maybe the boat is cheap they buy.
Tasha Sulaki says the former prime minister and transport minister should be prosecuted.
Meanwhile, the body of Nalui Kiriui's aunt, Vaefetu'u Mahe was one of only two recovered from the sinking.
Her husband and their two year old son also died in the tragedy.
Nalui Kiriui says while his family blame the Ashika's crew for the sinking, they are happy with the verdict.
She says it will help them a little to recover.
It's been pretty sad, a lot of tears and missing them and all that sort of stuff and it's hard as well. They trying to move on, it's really hard.
Nalui Kiriui, who lost an aunt, uncle and cousin in the Ashika sinking.