What does “I don’t see that there’s much to go on” mean?

Question

I don’t see that there’s much to go on.

Does it mean:

There is no reason to go on the discussion?

Or it means something else?

The fuller text is here:

It’s Ian who starts it, bluntly asking the attorney why he seems to be suggesting that Dana’s death might not have been an accident. [...]

“Very well,” David says, looking around at the rest of them, as if considering what to say. He takes a deep breath and exhales. “I don’t think that Dana’s death was an accident.” He pauses and adds, “In fact, I think she was pushed. And then I think her head was deliberately and forcefully smashed against the bottom stair.” [...]

“I think it’s a distinct possibility,” the attorney says crisply. Riley grips the arms of her chair tightly. She feels the tension build in the silent room; it’s palpable. Then Riley blurts out what they’re all thinking: “Did Matthew do it?” [...]

David turns to her and says, “I have no idea.” [...]

It seems to me,” Henry says, in his slightly pompous way, “that if this is a murder, it would be almost impossible to solve. It seems to have happened in the middle of the night. We were all asleep in our beds. There are no witnesses. Unless someone wants to confess, or share some helpful information about seeing someone creeping about in the night, I don’t see that there’s much to go on.”

An Unwanted Guest by Shari Lapena

Answer 1

I don't see that there's much to go on.

In my opinion there are few clues and they are not very good ones.

I don't see much = I see rather little

not much to go on = little to serve as a basis for proceeding further.

P.S. As Darren remarks in the comment, the "prosodic" emphasis falls on the word go:

There's not much to gó on.

Answer 2

Think of 'go' in a more general sense: There's not much to 'act' on. While they'd love to start investigating the mystery, the clues they have so far don't lend themselves to action on their part. A clue about a guy down the street we can track down and talk to? That's something to go on. The fact that the victim died at night? Unless you know someone who's third shift and wanders near where the victim was found, that information, while useful, is not actionable.