Unfortunately, levels are not a factor in the capture formula, unless you're using a Level Ball or a Nest Ball; otherwise, having a large level advantage won't help you.
Given the information you've given here, your chances of capturing the Murkrow in a Poké Ball or Premier Ball are roughly 10-12%; with a Great Ball it becomes about 16-20%. Given this, it's not at all unreasonable that you didn't catch it within ten Poké Balls, one Premier Ball and one Great Ball; it's mildly unlucky, but only mildly.
To improve your chances, be sure to use the best balls available to you (if you can buy Great Balls, then buy more) and put it to sleep if you can; otherwise, paralyze, poison or burn it (there's no reliable method to freeze an opponent, but that would be as good as sleep).
Here's a calculator you can use, and if you're interested in more information about how capturing works in the fourth-generation games, you can check out this page.
