看了本坛几位网友对协助警察逮捕了薛乃印的几位平民的评论，觉得古人说得“仗义每从屠狗辈，负心多是读书人。”确实有几分道理。若是当天薛乃印在阿拉巴马遇上的是本坛上的几位明哲保身的读书人，说不定现在他老人家还在全美国优哉游哉的晃荡呢。

当然，见义勇为、帮执法者抓嫌犯是一件危险的事情，大家应该量力而为。但是如果所有人都以自身会有危险为由，拒绝制止自己看到的犯罪行为的话，那么强盗在众目睽睽之下用刀捅倒刚从ATM取了钱的农妇、然后扬长而去，或者色狼在载满人的公车上强奸女子、然后全身而退，这种事情发生也就不是不可理解的了。-- 事实上，这种事已经在中国大陆发生过。我不能保证面对着有武器的强盗或强奸犯时，我会第一个挺身而出；但是，我至少不会在有人挺身而出之后去给挺身而出的人盖一顶“违法”或“违反人权”的帽子。

况且，在没有完全弄清楚薛是否真的受了伤之前，我们根本不能说那几位平民在拘留薛时过度使用了暴力。US Marshall 的人在新闻发布会上说的是：nobody got hurt:

http://video.msn.com/?mkt=en-au&brand=ninemsn&fg=rss&vid=77bd8ff6-73a6-4a91-b30e-3b76033d9166

Citizen\'s Arrest 是合法的，也就是说，这几位平民有权逮捕薛，这一点，相信大家都没有任何异议了。那剩下来的问题就是在逮捕疑犯的过程当中能使用多少 force 的问题了。

联邦法律中对这个问题的解读源于宪法第四修正案：

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

-U.S. Constitution: Fourth Amendment

也就是说，当有 probable cause 而嫌犯又是很明显的话，arrest 或 detention 就是合法的。第四修正案的条文本身没有明文规定执法者在 arrest 或 detain 犯人时可以使用多少 force，但是最高法院在1989年的一个判例对此有阐述：

Determining whether the force used to effect a particular seizure is reasonable under the Fourth Amendment requires a careful balancing of `the nature and quality of the intrusion on the individual\'s Fourth Amendment interests\' against the countervailing governmental interests at stake. Id., at 8, quoting United States v. Place, 462 U.S. 696, 703 (1983). Our Fourth Amendment jurisprudence has long recognized that the right to make an arrest or investigatory stop necessarily carries with it the right to use some degree of physical coercion or threat thereof to effect it. See Terry v. Ohio, 392 U.S., at 22 -27. Because [t]he test of reasonableness under the Fourth Amendment is not capable of precise definition or mechanical application, Bell v. Wolfish, 441 U.S. 520, 559 (1979), however, its proper application requires careful attention to the facts and circumstances of each particular case, including the severity of the crime at issue, whether the suspect poses an immediate threat to the safety of the officers or others, and whether he is actively resisting arrest or attempting to evade arrest by flight. See Tennessee v. Garner, 471 U.S., at 8 -9 (the question is whether the totality of the circumstances justifie[s] a particular sort of . . . seizure).

-U.S. Supreme Court, Graham v. Connor,
490 U.S. 386, 396 (1989)

也就是说，到底多少 force 算是 reasonable，是因案而易的，主要看的是三方面：

1. severity of the crime at issue -- 疑犯被控的罪行
2. whether the suspect poses an immediate threat to the safety of the officers or others -- 疑犯是否对执法者或他人有威胁
3. whether he is actively resisting arrest or attempting to evade arrest by flight -- 疑犯是否反抗或逃走

老薛被控杀妻、自称武术高手且跑了大半个地球，可算是三条都占全了。

以此看来，这几位仗义的屠狗辈抓老薛倒是完全合法的可能居多。