In watching GF1 last night on TCM, a question occurred to me:

Why did Tom say to Sollozzo that even Sonny wouldn't be able to call off Luca Brasi?

It seems to be very out of character for Tom to say something like that in general, and all the more inexplicable since Luca was pretending to be dissatisfied with the Corleones at that point. (Actually, he was dead, but Tom didn't know that.)

Was this just a mistake on Tom's part, or was there some angle he was working?

it was probably becuase we all from time to time find ourselves in situations where someone has an advantage over us. Our instinct is to say "Oh yea, well you forgot about this". It's a defense mechanism. Tom was just saying to Sollozzo that you may have killed the Don and you mayhave me in your clutches right now, but wait till Luca gets ahold of you. On the other hand, it could have been the lawyer in Tom trying to be explicit about the terms of the deal Sollozzo was proffering. You get the Corleones to back off and we can all work this out. Tom might have simply been advising Sollozzo that the Luca variable was out of the Family's control.

I think Tom was referring to the fact that Luca was totally and exclusively loyal to Vito, and reported directly to him--not through Tom, Sonny or the caporegimes. We saw this when, after the Sollozzo meeting, Vito said to Tom, "Send Luca Brasi to see me." And when he gave his order to Luca to "go to the Tattaglias, make them think that you're not too happy with our family, find out what he's got under his fingernails," he told it to Luca alone, without Tom or anyone else present. Therefore, Tom probably was telling Sollozzo the unvarnished truth when he said, "Even Sonny won't be able to call off Luca"--Sonny had no authority over Luca, and Luca would have been so outraged over the killing of his Don that nothing would stop him.

...and his loyalty and its explaination is explained in the book - giving weight to why Neri was Michael's Luca -

in both cases a man is backed into a wall and given an out by their respective Don's in exchange for loyalty and limitless violence if called on. Neither man drifted towards the Corleones and both started as the feared right hand - a wild card...

granted Neri went on to use his brain a bit more than his deadly skills, but the business changed quite a bit over the years

it was a scare tactic.....Tom knew that Luca was a feared man, and that he was loyal to Vito.....that was Vito's downfall, he asked Luca to go to the Tatallias and act unhappy.....they all knew it was a set up...so they were ready for Luca before he even got there.
So Tom was trying to get Solozzo to back off......that's all.

mayb , this is a little farfetched, tom was acting like he didnt know Luca had gone to the Tattaglias , unless I'm mistaken Vito/Luca dont tell anyone what ther doing, and he was just suggesting that Luca loved Vito and would kill anyone who dared harm him

remember vito seen luca privately

Good point A-Lee......I think you are correct, Tom may have been against that move had he had known the Don wanted to do that....

You may be onto something there. I hadn't considered that Tom may not have known of Luca's assignment. I couldn't imagine that Tom, no matter how much stress he was under, would reveal something that would sign Luca's death certificate.

But if he didn't know, it makes sense.

The theory that only Vito knew about Luca's assignment is bolstered by the confusion among the sons and the capos about his whereabouts after the shooting.

I might be wrong but I belive Luca said even though he was mad with the Corleones he still greatly respected Don Vito so he wouldn't really have been blowing Luca's cover also at that point Tom might have thought the task pointless now. And it could have been like you said the lawyer in Tom.

I think the last few posts reinforce what I said above. Tom was telling Sollozzo that Luca was only under the Don's control and that was one variable that Sollozzo need be aware of. Of course, that's why Sollozzo whacked him. As someone said above, the book makes it clear that Luca would never go against the Don and the story of Luca's unswerving loyalty to Vito was well known throughout gangland.