You should tread very carefully here. Recruitment companies are generally not stupid (I know, I know) and try very hard to protect themselves from someone stealing their contacts and depriving them of their commission. This one has been lax in their procedures and allowed you to identify the candidate- but that does not entitle you to merely "take" what you want. In the same way as if a shopkeeper forgot to lock their door at closing time that does not entitle you to walk in and take their stock.
Whether you wanted recommendations from a recruiter or not, by contacting a candidate they have advised you of, you are acting on their referral/recommendation. I am 100% convinced that you will find a clause in their Ts & Cs essentially describing that their fee becomes due if you employ any candidate for which they sent you details however that employment offer is reached. If present, and it is very likely to be present, this means that the very act of offering "their" candidate a job means that you have invoked their fee. You will probably notice that this clause has a 6 month or yearly timescale- In practise this means you could interview a candidate and not find them suitable and hence not offer, but in 11 months time remember them for a completely different job, salary, role etc, and offer them the job and the recruitment agency still has a right to their commission even though they did not place the candidate for the role... If you think it is far-fetched, then think again, I used to work for a recruitment agent (not as a recruiter I hasten to add), and I saw it acted upon. As I said, they are not (all) stupid and if they propose the candidate to the company they should be paid for that information.
Whether or not that is worth anyone's time in taking legal action is a different matter, and maybe they wouldn't take any action. But if they can prove they sent you the details, and the Ts & Cs and that you subsequently acted on that information, they will probably have a case. Such a case might be weakened if you have declined to enter into a contract with them by the point of offer to the candidate, but if you are declining to enter a contract you should not be offering their candidates, you can't have it both ways. Or rather, you can but you need to be aware of the risks. Once you and/or your company gets a reputation for "stealing" candidates you will find it hard to get terms from any recruitment company (yes they do talk to each other and share such information).